JPS5864221A - Manufacture of ferromagnetic iron oxide coated with cobalt - Google Patents

Abstract

PURPOSE:To obtain ferromagnetic iron oxide with high coercive force, favorable thermal characteristics and high aging stability by introducing P into crystals of ferromagnetic iron oxide and by depositing a compound contg. at least Co on the surfaces of the resulting ferromagnetic iron oxide particles. CONSTITUTION:An alkali such as sodium hydroxide is added to a ferrous salt soln. such as a ferrous sulfate soln. contg. suspended nuclear crystals of alpha- FeOOH, and while blowing air, the soln. is maintained at about 50-90 deg.C reaction temp. and 3-6pH so as to regulate the growing rate of the nuclear crystals to about 5-15g/l/hr and to grow the crystals about 1.5-6 times. In this stage, P is introduced almost uniformly into the crystals by adding a phosphorus compound such as o-phosphoric acid by 0.1-1wt% as P basing on the total amount of alpha-FeOOH produced finally. The resulting alpha-FeOOH contg. P is separated by filtration, washed in water, dried, and pulverized to obtain ferromagnetic iron oxide. This iron oxide is coated with about 0.5-10wt% compound contg. at least Co such as cobalt sulfate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cobalt-coated ferromagnetic iron oxide useful as a magnetic recording material. The ferromagnetic iron oxide is obtained by incorporating ') into the crystal in advance, and then applying a compound containing at least cobalt to the resulting ferromagnetic iron oxide. This invention relates to a method for producing ferromagnetic iron oxide.

Ferromagnetic iron oxide coated with a cobalt compound has a high coercive force, so it is widely used in the field of magnetic tracks such as video and audio. Many methods for obtaining ferromagnetic iron oxide have also been proposed. There are also several proposals for incorporating phosphorus into iron oxide before depositing cobalt.

For example, in Japanese Patent Publication No. 49-69588, 9 magnetite obtained by depositing phosphate etc. on α-1i"@oOH before being converted into madanetite Kl1 and reducing it, or I4 from fins. A method has been described in which a cobalt compound is deposited on the prepared r-F.108 and further tempered, but there is a drawback that the cobalt compound is not easily deposited uniformly.

Separately, 4I-Sho 55-149137 describes a method of adsorbing and diffusing cobalt compounds into crystals containing silicon and phosphorus, but mainly increases the specific surface area by adding silicon and phosphorus. Although a corresponding increase in coercive force has been observed, improvements are still desired in terms of variations in coercive force, etc.

The present invention differs from the above method in that the phosphorus compound is present in the crystal rather than on the particle surface, and α-F OOH, which does not contain silicon, is used, and a cobalt compound is deposited on the ferromagnetic iron oxide derived from it. This is considered to be a small percentage.

The inventors have found that the phosphorus contained in the crystal does not interfere with the deposition of the cobalt compound, resulting in a good and uniform cobalt coating, and that the phosphorus prevents the diffusion of cobalt into the crystal. As a result, it was confirmed that ferromagnetic iron oxide with high coercive force, excellent thermal properties, and stability over time could be produced.

The present invention produces a ferrous salt water I# solution containing α-F・OOH nucleus crystals suspended in the total α-FeOOHfiK that is finally produced.
On the other hand, in the presence of a phosphorus compound in an amount such that α1 to 1 weight- in terms of p, the nucleus crystals are grown by neutralization and oxidation to produce phosphorus-containing α-Fe00H, and the obtained α- peo
This is a method for producing cobalt-coated ferromagnetic iron oxide, which is characterized in that after inducing okl into ferromagnetic iron oxide, the surface of the ferromagnetic iron oxide particles is coated with a compound containing at least a small amount of cobalt.

α-F・0OHFi, for example, a ferrous salt solution is partially neutralized with an alkali to precipitate a part of F, and then oxidized to form α-
It is produced by generating F.OOH nucleus crystals, and then oxidizing this solution while neutralizing it with an alkali to grow the nucleus crystals. In the method of the present invention, a phosphorus compound is present in Kt during the nucleic crystal growth reaction.

The @1 iron salts used include ferrous sulfate, 1 iron nitrate,
Ferrous salts of mineral acids such as I11 iron chloride are preferred, and #i ferrous sulfate is preferred industrially.

Examples of alkalis include hydroxides, oxides, or carbonate groups of alkali metals or alkaline earth metals, such as sodium hydroxide, potassium hydroxide, sodium oxide, and calcium carbonate. Potassium oxide is preferred.Oxidizing agents used for oxidation include air, oxygen, and other oxidizing agents, with air generally preferred. Phosphorus compounds include orthophosphoric acid,
Phosphoric acid such as metaphosphoric acid, polyphosphoric acid, phosphorous acid, or
There are water-soluble salts of these alkali metals, ammonium, etc., and orthophosphoric acid or its salts are usually used.

The α-Fe00H nucleation reaction is usually performed at a reaction time of 30 to 100
To a ferrous salt solution with a concentration of 1 g/l, add the alkali necessary to bring the F ion in the mother liquor to 5-25 t/l, and raise the reaction temperature to 50-25 t/l while blowing air.
10-80, maintaining 100°C and pH between 3-8.
It takes place for a minute. In this step, when adding a K phosphorus compound to obtain nuclei crystals with good shape, α-F.
It is recommended to add a phosphorus compound to the mother liquor in an amount of 0.1 to 0.4 weight in terms of p relative to the OOH nucleus crystals, but this phosphorus is encapsulated in the nucleus crystals, and the phosphorus compound referred to in the present invention is does not exhibit the effect of

The subsequent α-FeOOH nucleus crystal growth reaction is usually carried out by adding an alkali to the ferrous salt solution in which α-F OOH nuclei are suspended, and then increasing the reaction temperature by blowing air into the ferrous salt solution at 50°C to
Maintaining the temperature at 90°C and the pH between 3 and 6, the growth rate of the nuclei is approximately 5 to 15 g/l/hour, and the growth rate is approximately 1.5 to 1.5.
It is carried out in lfc@ clause so that it is about 6. In this step, if a phosphorus compound is added to the mother liquor,
α-Fe0OHK can contain phosphorus uniformly. The amount of phosphorus compound added is determined by the total α
The p-conversion amount is 0.1 to 1% by weight based on the amount of -F600H. If this amount is too small, the desired effect will not be obtained; on the other hand, if it is too large, it will be difficult to obtain good thermal properties, stability over time, etc.

The phosphorus-containing α-Fe00H obtained in this way is made into α-P@00H powder through ordinary filtration, water washing, drying and pulverization, and this powder is subjected to ferromagnetic oxidation as referred to in the method of the present invention by an ordinary method. Iron, ie r-pesos, re@04 or bertolide compounds can be obtained. Dehydration is performed, for example, by heating in air to a temperature of 300 to 700°C, and reduction is performed, for example, with hydrogen or hydrogen containing water vapor at a temperature of 300 to 700°C.
Oxidation is carried out by heating to a temperature of 200-400°C, for example in oxygen or air.

In the method of the present invention, 1) the phosphorus-containing ferromagnetic iron oxide obtained by the above-described method is coated with a compound containing at least cobalt. This process is carried out by neutralizing the metal salt with an alkali in the iron oxide slurry. The cobalt salts used here include inorganic acid salts or organic acid groups of cobalt, such as cobalt sulfate, cobalt chloride, cobalt acetate, etc., and the amount of coating is usually based on the weight of iron oxide. The amount is 0.5 to 1 O-1, preferably 1 to 6%. At this time, metal salts other than cobalt that may be coated at the same time or before or after are @1 iron salt,
Examples include manganese salts, zinc salts, nickel salts, etc., and the amount of adhesion is usually 0.1% for ferrous iron compared to iron oxide.
5 to 201, preferably H5 to 1511T, 6, and 0 to 10 in the case of other metals.

Examples of methods for adhering include fl) a method of dispersing ferromagnetic iron oxide in a metal salt aqueous solution containing at least cobalt and adding an alkaline solution thereto; (2) a method of dispersing ferromagnetic iron oxide in a metal salt containing at least cobalt; (3) A method of dispersing ferromagnetic iron oxide in a mixture of an aqueous solution and an alkaline solution, (3) A method of dispersing ferromagnetic iron oxide in water, and adding thereto an aqueous metal salt solution containing at least cobalt and an alkaline solution; (4) Ferromagnetic A method of dispersing iron oxide in an aqueous alkaline solution and adding thereto an aqueous solution of a metal salt containing at least cobalt; (5) dispersing ferromagnetic iron oxide in an aqueous solution of a metal salt containing at least cobalt; Examples include a method of neutralizing dropwise addition, and it is also possible to treat part or all of cobalt, ferrous iron, and other metals simultaneously, sequentially, or adopt an appropriate method. The adhesion treatment may be carried out at room temperature or under heating at about 60 to 150°C.

The cobalt-coated ferromagnetic iron oxide obtained by the above method is subjected to plating, dried by a conventional method, heat-treated at about 100 to 300°C in a non-oxidizing or oxidizing atmosphere, and then dried. Good: The cobalt-coated ferromagnetic iron oxide obtained by the method of the present invention has a high coercive force and good thermal properties and stability over time. The reason for this is not clear, but ferromagnetic iron oxide with few pores can be easily obtained by heating phosphorus-containing α-F・00H at a relatively high temperature, and a large amount of phosphorus exists on the surface of ferromagnetic iron oxide, making it dangerous. It is presumed that this is because uniform and good cobalt deposition can be obtained, and that the phosphorus contained in the ferromagnetic iron oxide prevents cobalt from diffusing into the crystal, resulting in a preferable structure.

The following examples and comparative examples will provide a more detailed understanding of the present invention.

Examples 1-2 and Comparative Examples 1-2 3.800 g was placed in a reactor equipped with an air cooking tube and a stirrer.
204 of an aqueous solution containing FeSO4 was added, the temperature was raised to 43°C, 2.14j of a NaOH aqueous solution (concentration 200 g//) was added with stirring (precipitate F.15 r/l), and 60 (1 part hour) was added into the solution. Blow air at a speed of 45'C.
The mixture was reacted for 40 minutes to obtain α-paoo)I nucleus crystals.

Furthermore, while blowing air at a rate of 851 parts per hour,
Adding a predetermined amount of orthophosphoric acid and NaOH aqueous solution (concentration 200 g/1) FL4t shown in Table 1 below,
The pH was maintained at 5.1 and the reaction was carried out at 50° C. for 8 hours to grow the nucleus crystals approximately 3.5 times.

Each α-F 00H obtained by the above method is subjected to normal passing, water washing, drying and pulverization, and α-Fs00H
obtained as a powder, which was dehydrated (in air at 650°C) and reduced (in hydrogen containing water vapor at 420°C) by conventional methods.
) and oxidation (in air, 280℃) to obtain each γ
-F@@01 was obtained.

Each r-F@*Oa200 obtained by the above method
Disperse 21g of cobalt sulfate into a slurry in 21g of water, and add 120g of cobalt sulfate 17l/l solution while blowing KN into the liquid and gas.
- and 250 d of a 1 mol/l solution of ferrous sulfate was added and stirred.

Further, 780 - of a 5 mol/j solution of sodium hydroxide was added, and stirring was continued at room temperature (28°C) for 5 hours. The slurry after the reaction was filtered and washed with water, and the resulting slurry was dried at 110° C. for 10 hours in an inert atmosphere to obtain the desired cobalt-coated ferromagnetic iron oxide powders A-D.

Comparative Examples 3 to 4 Regarding α-F・OOHK obtained by the method of Comparative Example 1, -
After washing with filtration and water, a predetermined amount of orthophosphoric acid shown in the gt table below was applied to α-F・00HK, and r −F @tO was obtained in the same manner as in Example 1. Co-coated ferromagnetic iron oxide powders E and F were obtained.

The coercive force of the obtained samples A to FK was measured by a conventional method, and the thermal properties and stability over time were calculated by the following method to obtain the results shown in Table 1.

(Thermospecific measurement method) Room temperature and 12! ! 'Measure the coercive force at CK and determine the thermal characteristics using the following calculation.

(Fog room for stability over time) Measure the initial coercive force and the coercive force after leaving it for 10 days at 60° C. and relative humidity 80 degrees, and calculate the stability over time by using the lower calculation.

Temperature stability (ΔHa) = (initial coercive force) - (coercive force after standing for 10 days at m1 degree 60°C and relative humidity 80) Table 1 Example 3 9r obtained by the method of Example 1 Disperse 200 g of -F@*05 in water 21 to make a slurry, and while blowing N-rich gas into the liquid, add 1 mole of cobal sulfate/jl [12G11/
was added and stirred. Furthermore, sodium hydroxide 57 l/
Added 590 d of l solution and continued stirring at 90°C for 5 hours.
After the reaction, the slurry was passed through and washed with water, and the resulting slurry was dried at 110° C. for 10 hours to obtain the desired cobalt-coated ferromagnetic iron oxide powder H.

Example 4 Add 120 g of cobalt sulfate 17 l/l solution, stir,
Furthermore, 59 g of sodium hydroxide S5 mol/j solution is added, cobalt sulfate 1 mol/j+lI [120 m and manganous sulfate 17 mol/j solution 120 ml are added, stirred, and sodium hydroxide 57 mol/j solution is added. l solution 680m
Same as in Example 3 except for adding .
As a result, the desired cobalt-deposited ferromagnetic oxide ironwork was obtained.

Example 5 r-F 108 depositing cobalt and 111 iron compounds
of! Cobalt-coated magnetic iron oxide J was obtained in the same manner as in Example 1 except that K was replaced.

For Samples H, I, and J obtained above, the coercive force was measured using a conventional method, and the thermal properties and stability over time were calculated using the method described above to obtain the results shown in Table 2.

Claims (1)

[Claims] A ferrous salt aqueous solution containing α-F・OOH nucleus crystals suspended,
The nucleus crystals are grown by neutralization and oxidation in the presence of an amount of phosphorus compound that is 0.1 to 1 weight in terms of P based on the amount of 1-Fe00H that is finally produced. phosphorus-containing α
-F@OOH is generated and the obtained α-FeOOH is induced into ferromagnetic iron oxide, and then a compound containing at least cobalt is deposited on the surface of the ferromagnetic iron oxide particles. A method for producing ferromagnetic iron oxide.